Red-heads and Black-heads. New research finds the gene controlling head colour in the Gouldian Finch

The Gouldian Finch (Chloebia or Erythrura gouldiae) is famous for a number of reasons. The first is a sad one. It has become rare in its habitat of tropical northern Australia because of agricultural practice (burning grassland at the wrong time of year and the introduction of domestic livestock in areas which reason indicates should actually be left wild). The second is that it occurs in three colour morphs in the wild. The third is that because of its beauty it has always been a popular bird with aviculturists in Europe, North America and Japan.

The third reason (i.e. its popularity in aviculture) is responsible for the generation of so much knowledge about this species which has been put to good use in devising conservation measures  in the wild by halting, apparently, the precipitous decline in the size of the population and, even though only a few thousand birds of this small seed-eating bird remain, the possibly unwise lifting of its status from ‘Endangered’ to ‘Nearly Threatened’.

The breeding and maintenance of stocks of the Gouldian Finch in aviaries has also facilitated the recent discovery of the genetic mechanism responsible for the difference in head coloration of the morphs. For this article I am going to ignore the orange-headed morph which occurs at very low frequency (less than one in a thousand individuals). In the wild, the ratio of black-headed to red-headed individuals is 7:3.

From Toomey et al. 2018

Thanks to breeding records in captivity, it has been known for many years that the genetics of head colour can be explained by simple sex-linked Mendelian inheritance with the allele for red being dominant and black recessive. In 2016 this Red gene was located on the Z chromosome. In birds, the sex determination is not the same as in mammals. Male birds have two Z chromosomes, females one Z and one W.

Before going on to describe the very recent genomic work, I should point out that there are differences, discovered, again, by research on birds in captivity between the two colour morphs, in addition to the differences in head colour. Red heads are more aggressive and dominate in encounters with black heads. In competitive social environments, red heads show increased concentrations of testosterone and corticosterone in their blood whereas black heads do not. There is also assortative mating, red heads prefer red heads, blacks black. Clearly, whatever the genetic mechanism it is pleiotropic, i.e. affects a number of traits within the body.

A group of authors from U.S.A. and Portugal have now tracked down the locus of Red gene to a small region on the Z chromosome. The gene itself is on part of the chromosome that does not encode a protein that can be responsible for its actions in the body. However, it is in a position to control a nearby gene that encodes for the protein, Follistatin, and indeed the group provides evidence that it is the production of Follistatin which controls head colour as well as the other physiological traits. There is also evidence that Follistatin could be involved in controlling the differences in plumage colour between other species of bird.

There is still much work to be done on the ‘how’ or mechanistic questions as well as the ‘why’ questions such as why, given the stroppiness and dominance of the red-head over the black, the overall ratio of 3:7 has remained unchanged.

Finally, since you ask, have I ever seen in Gouldian Finch in the wild? No. Even though I have been to northern Australia several times and passed through their known range, I have not had the chance to go to one of the known hot-spots of the remaining population.

Toomey MB, Marques CI, Andrade P, Araújo PM, Sabatino S, Gazda MA, Afonso S, Lopes RJ, Corbo JC, Carneiro M. 2018 A non-coding region near Follistatin controls head colour polymorphism in the Gouldian finch. Proceedings of the Royal Society B 285, 20181788. http://dx.doi.org/10.1098/rspb.2018.1788

Legge S, Garnett S, Maute K, Heathcote J, Murphy S, Woinarski JCZ, Astheimer L. 2015. A landscape-scale, applied fire management experiment promotes recovery of a population of the threatened Gouldian Finch, Erythrura gouldiae, in Australia’s Tropical Savannas. PLoS ONE 10(10): e0137997. doi:10.1371/journal.pone.0137997

Classic Reads:

Mike Fidler (who has made enormous financial and practical contributions to the conservation and study of the Gouldian Finch in Australia an UK) and Stewart Evans (1936-2010) late of the University of Newcastle, UK. The Gouldian Finch. 1986. Blandford Press.

Derek Goodwin (1920-2008). 1982. Estrildid Finches of the World. London: British Museum (Natural History) and Oxford University Press.

Gouldian Finches have been kept and bred since the 1870s. This drawing
illustrates an article on cage-bird traffic of the U.S.A. by Henry Oldys
published in the Yearbook of the U.S. Department of Agriculture 1906